Uterine leiomyomata (UL), also called fibroids, are the most common pelvic tumors in females. Although benign neoplasms, UL constitute a major public health problem as 20-25% of affected women experience debilitating symptoms including excessive menstrual bleeding, pelvic discomfort, and reproductive failure. Medical treatment options for UL are limited, and surgery is the mainstay of therapy. In fact, UL are the most common indication for hysterectomy accounting for over 200,000 procedures annually in the United States. Although it is well recognized that UL are steroid-dependent tumors, much remains to be known about their growth and development. Compelling evidence suggests a genetic liability to develop UL. These tumors are at least three times more frequent in black than in white women, and twin-pair correlations for hysterectomy in monozygotic twins are about twice that observed in dizygous twins. Studies of familial aggregation indicate a 2.5-fold increased risk for UL among first-degree relatives of affected probands compared to relatives of unaffected probands; this odds ratio increases to 5.7 after stratifying cases by age of proband (< 45 years) and of relatives (less than or equal to 40 years). About 25-40% of UL are karyotypically abnormal, and several genes involved in the pathobiology of the tumors have been identified using positional cloning approaches based on chromosome rearrangements. Genetic linkage analysis in two rare Mendelian disorders, Reed syndrome (MIM150800), characterized by UL in association with multiple cutaneous leiomyomata, and hereditary leiomyomatosis and renal cell cancer (HLRCC, MIM605839), a cancer syndrome characterized by uterine leiomyomas and papillary renal cell carcinoma, resulted in the surprising finding of mutations in the gene for fumarate hydratase. Despite these important findings, we remain ignorant of the genes that predispose millions of women to develop these tumors. Experiments in this application will focus on identification, isolation and characterization of genes involved in the pathogenesis of UL. Specifically, we propose to identify genes that predispose women to develop UL by performing a genome-wide scan (www.fibroids.net: "Finding Genes for Fibroids"). Ultimately, understanding genetic pathways involved in the formation of UL may lead to I improved treatment options for affected women and lifestyle changes for at risk individuals.